1. Field of the Invention
The present invention relates to a method for manufacturing an armature used in print heads in wire dot matrix printers.
2. Discussion of the Background
In a print head in a wire dot matrix printer, an armature connected to printing wires is turned between a printing position and a waiting position. When the armature is turned to the printing position the tips of the wires strike a printing medium such as paper to perform printing. Print heads of this type wire dot matrix printer contain a coil that generates a magnetic flux around an armature to form a magnetic circuit capable of attracting the armature from the waiting position to the printing position.
The armature includes an arm and magnetic circuit forming members attached to both side surfaces in the thickness direction of the arm. A printing wire is attached to the arm by brazing. The magnetic circuit forming members are attached to the arm by a method such as spot welding. Technology for welding an armature to another member is disclosed in JP-U 35288/1993 and JP-A 314868/1997. Technology for welding three members together is disclosed in JP-B 22994/1995.
The arm and magnetic circuit forming members are in most cases plated to prevent corrosion and to improve capability for brazing. The strength of the joint between the arm and magnetic circuit forming members welded to the arm therefore weakens due to the plating and the nugget region becomes smaller. The magnetic circuit forming members welded in this state to the arm are prone to easily separate from the arm, and the armature has only a short service life.
Faster printing speeds attained in recent years have increased the need for lightweight armatures. The arm of the lightweight armature is made as thin as possible to reduce the inertial momentum caused by the vibration. The arm and the magnetic circuit forming members of the armature are also being made smaller in size or miniaturized. The smaller size of the arm and magnetic circuit forming members makes them difficult to spot weld so that the connecting joint does not have sufficient strength to withstand the swing of the armature.